The long-range goal of our research is to understand the process by which simian virus 40 (SV40) acts to transform cells growing in tissue culture and to cause tumors in animals. We propose to examine the roles that SV40-coded proteins may play in transformation and oncogenicity. By understanding the mechanism of SV40 oncogenesis, we may move closer to an understanding of human cancer. Our specific aims are to use SV40 "early" region deletion mutants that we have isolated to discover which SV40 functions are involved in the maintenance of transformation of cells in culture. We hope to answer three questions: 1) Which protein(s) coded for by our deletion mutant, d1536, is required for the maintenance of transformation? This mutant contains a large deletion in the early region of SV40 and yet is still able to maintain transformation. We will first expand this deletion to determine the minimum amount of SV40 genetic information required for transformation. We will then investigate which protein(s) is coded for by the early region of this new "minimum transforming mutant", dlmin. 2) Are cells transformed by dlmin tumorigenic? We will test cells transformed by dlmin for their ability to cause tumors in immunodeficient (nude) mice and hamsters. 3) What is the mechanism by which SV40 transforms cells and causes tumors? We will attempt to isolate a temperature-sensitive version of dlmin that is temperature sensitive for the maintenance of transformation and will use dlmin and tsdlmin to identify functions that these mutants can perform that may be responsible for their ability to transform. We will examine the intracellular location of the transforming proteins. Of these mutants and will use purified mutant transforming proteins to assay for activities suggested by the localization experiments. Since dlmin will have such a limited amount of genetic information with which to encode an oncogenic protein, the transforming protein of dlmin is expected to be quite small (molecular weight loss than 25K). Therefore, any activities of this small protein that we can identify should be strong candidates for the oncogenic activity of dlmin.